[time-nuts] No more 60Hz, How do I discipline 120VAC 60Hz from a UPS

[Will Matney]

Chris,

Yup, that's all I did. Use the line to keep the batteries charging, and
when the line goes down, the battery or batteries just keep on supplying
the system. Mine wasn't a sine wave though, but a modified square wave,
however it worked like a charm.

I got the idea from a website, and modified it to my taste, but it really
didn't cost much with all the surplus transformers available, and there is
a huge number available with high power ratings. I used a bank of NPN
switching transistors, and I forget what they were, but they had slightly
higher ratings than a 2N3055. There was a driver circuit between them and
the chip. I can't remember if Maxim, or another, made the IC, as I would
have to try to find my info on the supply, because I sold it about two
years after I finished it.

One could try to find an older sine wave UPS, and modify it, but it would
need to be a 60Hz output supply, because the transformer would be sized
incorrectly, with a higher frequency rating, when dropping it down to 60
Hz. As John mentioned earlier, the el-cheapo inverters are pretty much
junk, and run as high as 1 kHz, if I recall. They were made to run small
TV's, etc, that don't require a fixed line frequency, since they all have
hot chassis now that don't use isolation transformers.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 6/25/2011 at 11:55 AM Chris Albertson wrote:

>> The reason for using 12 Vdc, is that you can pick them up, and 24 Vac CT
>> transformer, on the cheap
>
>That's a good point.    So use two of them.  One to power a high
>current amp that produces a 12V AC signal from a high precision 60Hz
>input.  Then the other to convert the 12V to 120V.  This avoids the
>need for a high voltage DC power supply.  Likely cuts the total cost
>in half at least.     So just use use 12V supply to the amp and then a
>cheap 12V transformer connected "backwards" to step up to the desired
>voltage.
>
>The second advantage of this design is that you can connect a lead
>acid gell cell battery in parallel to the 12V DC supply and if the AC
>fails the battery will power the amp for a while.   This way there is
>no switching so the 60Hz wave remains continuously even if AC mains
>fails.
>
>This is something most UPS don't do but for this application you don't
>want the  60Hz sine wave to be broken.
>
>As long as the load is only a few milliamps of AC this should not be
>hard to do.
>
>
>-- 
>
>Chris Albertson
>Redondo Beach, California
>
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